The invention relates to a sports shoes, more especially to sports shoes with resilient, highly elastic heels.
During most kinds of modern competitive sports, such as basketball, volleyball, tennis and other games requiring the participants to run and to jump, the impact between foot and floor is hard, and particularly hard on the heel. This impact ofter leads to injuries to the human body, mostly parts of the feet and legs, and many joggers and runners suffer from knee injuries due to the sudden shock transferred from the heel to the relatively soft cartilage of the knee. To sum up, there happen to occur innumerable injuries to the ankle, the knee and to the vertebrae of the spinal column, owing to non-elastic shoes worn by the sportsman.
In order to prevent these kinds of injuries, as far as possible, there exist many types of sports shoes provided with elastic heels. Since it became evident that a solid heel made from an elastomer does not give the desired relief by spring action, most modern sports shoes now have heels provided with air-filled cavities. The air in the cavity or cavities is purported to be compressed by impact of the heel with the floor and to be expanded immediately upon lifting of the shoe, in order to be prepared for the next impact. There exist heels with open or with closed air-filled cavities, but it has been found that their efficiency is minimal for the following reasons: increase of air pressure in the cavity is effected by a very small heel deflection and results in a relatively small working travel; even taking into account the compression of the cartilage the impact shock is, nevertheless, not sufficiently damped to prevent an injury or a permanent incapacity to the sportsman or sportswoman.
In order to increase the elasticity of the heel material some sport shoes include metal springs inserted into suitable heel cavities, and some modern embodiments of this kind are disclosed in U.S. Pat. No. 4,638,575 (Illustrato), U.S. Pat. No. 4,843,737 (Vorderer), and U.S. Pat. No. 4,881,329 (Crowley). However, since in these embodiments the shoe is flat, i.e. the heel and the sole lie in the same flat surface, the springs do not add much to the elasticity of the heel, the more as the parts in front and to the rear ofthe cavity are made of soild material, such as rubber, and do contribute very little to the total deflection.
The present invention has the object to provide a sports shoe with a heel of great elasticity, owing to a long deflection and, accordingly, high gradual compression rate.
It is another object to provide a sports shoe with a heel which will return to its original shape immediately upon removal of the load, as soon as the foot is lifted off the ground, with the aim of reducing the shock to the body and to return to the runner more energy than obtainable with conventional shoes.
It is another object to provide a heel with spring means for ready inclusion in a cavity, in order to increase its elasticity.
It is an alternative object to provide springs of various load and compression factors for alternative insertion into a cavity of the heel for use of the same shoe for different kinds of sports or adaptation of the same shoe size to persons of different weight.
And it is a final object to produce this kind of sports shoe at low cost with a view to keeping their price at a level with the known, conventional brands.